Azurite and Malachite (#38)
|North America||Apex Mine, St. George, Washington Co., Utah, USA||3 ¾" x ½" x ½"|
Well, there are so many specimens of azurite and/or malachite in this display that we are running out of different things to say about them, but this one is interesting.
The Apex Mine, in the Beaver Dam Mountains near St. George, Utah, opened in 1884, and it produced mostly copper and silver until 1962. Along with these were minor amounts of gold and lead. (Just by way of explanation, when one says that a mine produced copper or some other metal, that usually does not mean that it produced chunks of pure metal. Instead it produced ore minerals that contained that metal in their chemical compositions, and then the ore had to be processed, by various physical and chemical processes, to extract the metal of interest.) In 1985 the mine was reopened to mine for minerals containing germanium and gallium, elements of importance in semiconductors, electronics, and the medical field.
Now, to this hollow cast of malachite and azurite. A cast is what is produced by a mold. Think of a Jello mold - the Jello inside, when dumped out, is a cast of the mold. A cast such as this one may result when one mineral coats another and then the original mineral dissolves, leaving the center empty. (Unlike the jello "cast" inside the mold, this is an exterior cast, or epimorph – meaning "forms upon". Think of the cast on a broken arm. The arm is a mold for the exterior cast. If the arm is slid out, the hollow cast remains.) In this case it is hard to tell whether both malachite or azurite coated whatever has dissolved, or whether azurite coated the original mineral and then was partially replaced by malachite. The Learn More for specimen #37 contains the reaction that results in malachite replacing azurite, and it discusses the phenomenon called pseudomorphism.